This invention relates to apparatus for ventilation and temperature control of an enclosed space or compartment of a vehicle, such as the driving and/or passenger compartments of cars, lorries, and trucks.
Such apparatus is known in which the flow of air to the compartment is controlled by pivoted flap valves, so that the amount of air can be controlled by said valves, e.g. to control the heating of the compartment. The selective operation of a plurality of such valves is also known from U.S. Pat. Nos. 3,656,541 and 3,948,312 for the purpose of varying the relative flows through two different outlets to different parts of the same compartment.
A disadvantage of such known apparatus using pivoted flap valves, however, is that the forces required to be applied to the valves varies, and in particular a relatively large effort may be required to hold a valve on its seating when it is required to stop the airflow. This problem is increased by the fact that it is usually impossible to arrange that the controlling transmission linkage to the valve is at its most efficient angle when the valve is in the closure position. It is also the case that when the apparatus has a number of such valves that are required to be displaced differently, as for varying the relative flows through two different outlets, the mechanical transmission of the operating movements from a control means that co-ordinates the valve settings can be complicated.
It is, moreover, difficult to obtain sufficiently precise control of such pivoted flap valves at small openings. In a conventional flap valve the relationship between airflow and angular opening setting is not linear, the flow rate increasing very rapidly as the valve begins to open and being little affected by changes of setting at large openings.